Development of cement based strain sensor for structural health monitoring

Earthquaqes, material degradations, environmental effects and user blames affect structural safety negatively. Health monitoring is crucial for human life safety. Typical metal strain gages used for this purpose, measure from the surface of structure. Measurement inside of the structural member with metal straingages is challenging and might contains error probability. Standart strain gages have short life time because of delicacy. Therefore big amounts are needed to monitor the structure which brings high costs. In this study 31 different mixes designed, 10 contain steel fibers, 20 contain carbon fibers and 1 mix contains no fiber. Every mixture has different fiber lenght and volumetric ingredient ratios. All mixes were tested with compression and split tensile tests. Tree 5 cm cubic samples were molded from every mix design for both mechanical tests. In totaly 186 samples were molded and tested. Through mechanical tests, change in electrical resistivity of cement based strain sensor (CBS) due to strain was investigated. Mixture that the most sensitive to strain is offered as CBS. Sensor properties of CBS which sensitivity, linearity, limit strain as characteristic values were determined. Mechanisms inside the sample matrix were enlightened under compression and split tensile test. CBS is 22 times more sensitive to strain than typical metal strain gages. As a cement based material CBS can be position easly in concrete structural member. By means of this advantage CBS can measure from inside of structural member by high precision and low error. Due to being in conrete CBS is less affected than metal strain gages from environmental negative influences. This property makes CBS advantageous about life time and cost issues. With long life time and low costs CBS will generalize structural health monitoring and decrease loss of life and property.